quota: Ensure qids map to the filesystem

Introduce the helper qid_has_mapping and use it to ensure that the
quota system only considers qids that map to the filesystems
s_user_ns.

In practice for quota supporting filesystems today this is the exact
same check as qid_valid.  As only 0xffffffff aka (qid_t)-1 does not
map into init_user_ns.

Replace the qid_valid calls with qid_has_mapping as values come in
from userspace.  This is harmless today and it prepares the quota
system to work on filesystems with quotas but mounted by unprivileged
users.

Call qid_has_mapping from dqget.  This ensures the passed in qid has a
prepresentation on the underlying filesystem.  Previously this was
unnecessary as filesystesm never had qids that could not map.  With
the introduction of filesystems outside of s_user_ns this will not
remain true.

All of this ensures the quota code never has to deal with qids that
don't map to the underlying filesystem.

Cc: Jan Kara <jack@suse.cz>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index ff21980d0119a58aa41c825258e435aa799042c7..74706b6aa74747279fe7d87defd7bae2fadca030 100644 (file)
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -841,6 +841,9 @@ struct dquot *dqget(struct super_block *sb, struct kqid qid)
        unsigned int hashent = hashfn(sb, qid);
        struct dquot *dquot, *empty = NULL;
 
+       if (!qid_has_mapping(sb->s_user_ns, qid))
+               return ERR_PTR(-EINVAL);
+
         if (!sb_has_quota_active(sb, qid.type))
                return ERR_PTR(-ESRCH);
 we_slept:

diff --git a/fs/quota/quota.c b/fs/quota/quota.c
index 0f10ee9892ce3a371b5341ebc4f1db2bd5a74a8a..73f6f4cf0a210791570ee3e370a17c3665c98a93 100644 (file)
--- a/fs/quota/quota.c
+++ b/fs/quota/quota.c
@@ -211,7 +211,7 @@ static int quota_getquota(struct super_block *sb, int type, qid_t id,
        if (!sb->s_qcop->get_dqblk)
                return -ENOSYS;
        qid = make_kqid(current_user_ns(), type, id);
-       if (!qid_valid(qid))
+       if (!qid_has_mapping(sb->s_user_ns, qid))
                return -EINVAL;
        ret = sb->s_qcop->get_dqblk(sb, qid, &fdq);
        if (ret)
@@ -237,7 +237,7 @@ static int quota_getnextquota(struct super_block *sb, int type, qid_t id,
        if (!sb->s_qcop->get_nextdqblk)
                return -ENOSYS;
        qid = make_kqid(current_user_ns(), type, id);
-       if (!qid_valid(qid))
+       if (!qid_has_mapping(sb->s_user_ns, qid))
                return -EINVAL;
        ret = sb->s_qcop->get_nextdqblk(sb, &qid, &fdq);
        if (ret)
@@ -288,7 +288,7 @@ static int quota_setquota(struct super_block *sb, int type, qid_t id,
        if (!sb->s_qcop->set_dqblk)
                return -ENOSYS;
        qid = make_kqid(current_user_ns(), type, id);
-       if (!qid_valid(qid))
+       if (!qid_has_mapping(sb->s_user_ns, qid))
                return -EINVAL;
        copy_from_if_dqblk(&fdq, &idq);
        return sb->s_qcop->set_dqblk(sb, qid, &fdq);
@@ -581,7 +581,7 @@ static int quota_setxquota(struct super_block *sb, int type, qid_t id,
        if (!sb->s_qcop->set_dqblk)
                return -ENOSYS;
        qid = make_kqid(current_user_ns(), type, id);
-       if (!qid_valid(qid))
+       if (!qid_has_mapping(sb->s_user_ns, qid))
                return -EINVAL;
        /* Are we actually setting timer / warning limits for all users? */
        if (from_kqid(&init_user_ns, qid) == 0 &&
@@ -642,7 +642,7 @@ static int quota_getxquota(struct super_block *sb, int type, qid_t id,
        if (!sb->s_qcop->get_dqblk)
                return -ENOSYS;
        qid = make_kqid(current_user_ns(), type, id);
-       if (!qid_valid(qid))
+       if (!qid_has_mapping(sb->s_user_ns, qid))
                return -EINVAL;
        ret = sb->s_qcop->get_dqblk(sb, qid, &qdq);
        if (ret)
@@ -669,7 +669,7 @@ static int quota_getnextxquota(struct super_block *sb, int type, qid_t id,
        if (!sb->s_qcop->get_nextdqblk)
                return -ENOSYS;
        qid = make_kqid(current_user_ns(), type, id);
-       if (!qid_valid(qid))
+       if (!qid_has_mapping(sb->s_user_ns, qid))
                return -EINVAL;
        ret = sb->s_qcop->get_nextdqblk(sb, &qid, &qdq);
        if (ret)

diff --git a/include/linux/quota.h b/include/linux/quota.h
index 9dfb6bce8c9eb08f0c45a8d1b76f86b0b489b30e..1db16ee39b318fe2a796669c08bed266b94281e5 100644 (file)
--- a/include/linux/quota.h
+++ b/include/linux/quota.h
@@ -179,6 +179,16 @@ static inline struct kqid make_kqid_projid(kprojid_t projid)
        return kqid;
 }
 
+/**
+ *     qid_has_mapping - Report if a qid maps into a user namespace.
+ *     @ns:  The user namespace to see if a value maps into.
+ *     @qid: The kernel internal quota identifier to test.
+ */
+static inline bool qid_has_mapping(struct user_namespace *ns, struct kqid qid)
+{
+       return from_kqid(ns, qid) != (qid_t) -1;
+}
+
 
 extern spinlock_t dq_data_lock;